The DUP has historically strong links to Protestant churches, particularly the Free Presbyterian Church of Ulster (the church Paisley founded) and has traditionally been regarded as the more Ulster loyalist of the two large unionist parties. However, this influence reduced somewhat under the Robinson leadership in an attempt to reach out to non-Protestants, particularly socially conservative Catholics.[7][8]

The DUP is the largest party in Northern Ireland, holding eight seats at Westminster and 38 seats in the Northern Ireland Assembly. It has one seat in the European Parliament, where its MEP, Diane Dodds, sits as a Non-Inscrit.

Although the party is primarily active in Northern Ireland politics, during 2004–05 it had one representative from the English constituency of Basingstoke, as a result of a defection to the party.

The DUP also holds seats in the House of Commons of the United Kingdom, and has been elected to each of the Northern Ireland conventions and assemblies set up since the party's creation. It has long been the principal rival to the other major unionist party, the UUP (known for a time in the 1970s and 1980s as the Official Unionist Party (OUP) to distinguish it from the then multitude of other unionist parties, some set up by deposed former leaders). The DUP's main opponent is Sinn Féin and its main rival for votes is the Ulster Unionist Party.

The Good Friday Agreement relied on the support of a majority of unionists and a majority of nationalists in order for it to operate.[citation needed] During the 2003 Assembly Election, the DUP argued for a "fair deal" that could command the support of both unionists and nationalists. After the results of this election the DUP argued that support was no longer present within unionism for the Good Friday Agreement. They then went on to publish their proposals for devolution in Ireland entitled Devolution Now.[14]

These proposals have been refined and re-stated in further policy documents including Moving on[15] and Facing Reality.[16] The DUP holds the view that any party which is linked to a terrorist organisation should not be eligible to hold Government office.[citation needed]

The DUP fought the resulting election to the Northern Ireland Legislative Assembly and took two seats in the multi-party power-sharing executive. While serving as ministers, they refused to sit in at meetings of the Executive Committee in protest at Sinn Féin's participation.[citation needed] The Executive ultimately collapsed over an alleged IRA espionage ring at Stormont (see Stormontgate).

In the delayed Northern Ireland Assembly election of 2003, the DUP became the largest political party in the region, with 30 seats. In 2004, it became the largest Northern Ireland party at Westminster, with the defection of former UUP MP Jeffrey Donaldson. On 12 December 2004, English MP Andrew Hunter took the DUP whip, giving the party seven seats, in comparison to the UUP's five, Sinn Féin's four, and the Social Democratic and Labour Party's (SDLP) three.

In the 2005 general election, the party reinforced its position as the largest unionist party, winning nine seats, making it the fourth largest party in terms of seats in the British House of Commons behind Labour, the Conservatives and the Liberal Democrats. In terms of votes, the DUP was the fourth largest party on the island of Ireland.

On 27 October 2006, the DUP issued a four-page letter in the Belfast Telegraph newspaper asking "Are the terms of Saint Andrew's a basis of moving forward to devolution?", with responses to be received to its party headquarters by 8 November. It was part of the party's policy of consultation with its electorate before entering a power-sharing government.[citation needed]

On 24 November 2006, Ian Paisley refused to nominate himself as First Minister of Northern Ireland designate. There was confusion between all parties whether he actually said that if Sinn Féin supported policing and the rule of law that he would nominate himself on 28 March 2007 after the Assembly elections on 7 March 2007. The Assembly meeting was brought to an abrupt end when the building had to be evacuated because of a security breach. Paisley later released a statement through the press office stating that he did in fact imply that if Sinn Féin supported policing and the rule of law, he would go into a power-sharing government with them. This was following a statement issued by 12 DUP MLAs stating that what Ian Paisley had said in the chamber could not be interpreted as a nomination.[18]

In February 2007, the DUP suggested that it would begin to impose fines up to £20,000 on members disobeying the party whip on crucial votes.[19]

On 24 March 2007 the DUP party executive overwhelmingly endorsed a resolution put to them by the party officers which did not agree to an establishment of devolution and an executive in Northern Ireland by the Government's deadline of 26 March, but did agree to setting up an executive on 8 May 2007.[9]

On 27 March 2007, the party's sole Member of the European Parliament (MEP), Jim Allister, resigned from the party, in opposition to the decision to enter a power-sharing government with Sinn Féin. He retained his seat as an independent MEP as leader of his new hard-line anti-St Andrews Agreement splinter group that he formed with other disaffected members who had left the DUP over the issue, Traditional Unionist Voice, a seat which he retained until Diane Dodds won the seat back for the DUP in 2009. MP Gregory Campbell warned on 6 April 2007 that his party would be watching to see if benefits flow from its agreement to share power with Sinn Féin.[20]

On 31 May 2008, the party's central Executive Committee met at the offices of Castlereagh Borough Council where Ian Paisley formally stepped down as party leader and Peter Robinson was ratified as the new leader, with Nigel Dodds as his deputy.

On 11 June 2008 the party supported the government's proposal to detain terror suspects for up to 42 days, leading to The Independent dubbing all of the party's nine MPs as part of "Brown's dirty dozen".[21]The Times reported that the party had been given "sweeteners for Northern Ireland" and "a peerage for the Rev Ian Paisley", amongst other offers, to secure Gordon Brown's bill.[22]

Members of the DUP were lambasted by the press and voters, after MPs' expenses reports were leaked to the media. Several newspapers referred to the "Swish Family Robinson" after Peter Robinson, and his wife Iris, claimed £571,939.41 in expenses with a further £150,000 being paid to family members.[23] Further embarrassment was caused to the party when its deputy leader, Nigel Dodds, had the highest expenses claims of any Northern Ireland MP, ranking 13th highest out of all UK MPs.[24] Details of all MPs' expenses claims since 2004 were published in July 2009 under the Freedom of Information Act 2000.

In January 2010, Peter Robinson was at the centre of a high-profile scandal relating to his 60-year-old MP/MLA wife Iris Robinson's infidelity with a 19-year-old man, and alleged serious financial irregularities associated with the scandal.[25][26]

In the 2015 General Election, when the result was expected to be a hung parliament, the issue of DUP and the UK Independence Party forming a coalition government with the UK Conservative Party was considered by Nigel Farage (leader of UKIP).[27][28] The then Deputy Prime Minister and leader of the Liberal Democrats, Nick Clegg, warned against this "Blukip" coalition, with a spoof website highlighting imagined policies from this coalition – such as reinstating the death penalty, scrapping all benefits for under 25s and charging for hospital visits.[29] Additionally, issues were raised about the continued existence of the BBC (as the DUP, UKIP and Conservatives had made a number of statements criticising the institution)[30] and support for LGBT rights and same-sex marriage.[31][32] However, in an interview with BBC Radio 5 Live deputy leader of the DUP Nigel Dodds told BBC Newsline in 2015 that, despite opposition to same-sex marriage, the DUP was "against discrimination based on religion ... or sexual orientation".[32] Additionally, David Cameron said he "totally disagreed" with the DUP on the issue of same-sex marriage and LGBT rights, claiming that "nothing I will do" would go against the principle of "the values that I have", including "equality for gay and lesbian people".[33]

On 10 September 2015, Peter Robinson stepped aside as First Minister and other DUP ministers, with the exception of Arlene Foster, resigned their portfolios.[34]

On 4 October 2016, DUP leader Arlene Foster and DUP MPs held a champagne reception at the Conservative Partyconference, marking what some have described as an "informal coalition" or an "understanding" between the two parties to account for the Conservatives' narrow majority in the House of Commons.[35][36]

The following information is correct for the Northern Ireland Executive in October 2016. They are in a mandotary power sharing government with Sinn Féin who occupy the rest of the Ministries with the exception of Justice which is held by independent unionist MLA Claire Sugden. See Northern Ireland Executive.

^Beyond the Sectarian Divide: the Social Bases and Political Consequences of Nationalist and Unionist Party Competition in Ireland by Geoffrey Evans and Mary Duffy. In British Journal of Political Science, Vol. 27, No. 1. (Jan. 1997), p.58